The following documents and standards descriptions are hereby incorporated into the present disclosure as if fully set forth herein: 1) 3GPP TS 36.211 v11.2.0; 2) 3GPP TS 36.212 v11.2.0; 3) 3GPP TS 36.213 v11.2.0; 4) 3GPP TS 36.331 v11.2.0; 5) R1-125402, 3GPP TS 36.211 CR; and 6) R1-125404, 3GPP TS 36.213 CR. Channel quality indicator (CQI) is defined in section 7.2.3 of 3GPP TS 36.213 v11.2.0. Differential CQI is described in section 7.2 of 3GPP TS 36.213 v11.2.0. A channel state information (CSI) process is described in 3GPP TS 36.331 v11.2.0. Physical uplink control channel (PUCCH) mode 1-1 is described in section 7.2.2 of 3GPP TS 36.213 v11.2.0. PUCCH mode 2-1 is also described in section 7.2.2 of 3GPP TS 36.213 v11.2.0.
In 3GPP LTE-Advanced standards, wide beam patterns are used for CSI-RS transmissions. The beam (virtualization) patterns of antenna ports are transparent to the user equipment (UEs). The UEs may not know or need to know the virtualization pattern for transmission/reception. A channel coefficient from each CSI reference signal (RS) port to a UE may correspond to a composite response of multiple paths, and is often frequency selective. The UE estimates channel coefficients relying on CSI-RS, and then using the estimated channels to calculate various parameters including precoding matrix indicator (PMI), rank indicator (RI) and CQI (for <=8 CSI-RS ports) or PMI, RI, precoding type indicator (PTI) and CQI (for 8 CSI-RS ports) according to enhanced Node B (eNB) (e.g., base station (BS)) configuration.
When all CSI-RS ports have wide beams, the average power of signals received from the CSI-RS ports is on a similar order. The similar power levels partially motivated constant-modulus precoding matrices/vectors in legacy LTE codebooks in 3GPP TS 36.211 and 36.213. When a vector/matrix is constant-modulus, all the elements of each vector/matrix have the same magnitude.
Accordingly, there is a need for improved communication techniques and standards in advanced wireless communication systems.